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                <h1 id="1、JS基础"><a href="#1、JS基础" class="headerlink" title="1、JS基础"></a>1、JS基础</h1><h2 id="1、js的组成"><a href="#1、js的组成" class="headerlink" title="1、js的组成"></a>1、js的组成</h2><table>
<thead>
<tr>
<th><strong>组成部分</strong></th>
<th><strong>作用</strong></th>
</tr>
</thead>
<tbody><tr>
<td><strong>ECMA Script</strong></td>
<td>构成了JS核心的语法基础(简称es)es6</td>
</tr>
<tr>
<td><strong>BOM</strong></td>
<td>Browser Object Model <font color="red">浏览器对象模型</font>，用来操作浏览器上的对象<br>window、navigator 、screen 、history 、location 、document、 event等；</td>
</tr>
<tr>
<td><strong>DOM</strong></td>
<td>Document Object Model <font color="red">文档对象模型</font>，用来操作网页中的元素（标签）</td>
</tr>
</tbody></table>
<p><img src="https://gitee.com/ergou15154/drawing-bed/raw/master/source/image-20210828203133499.png" alt="image-20210828203133499"></p>
<h2 id="2、js引入的2种方式"><a href="#2、js引入的2种方式" class="headerlink" title="2、js引入的2种方式"></a>2、js引入的2种方式</h2><pre class="line-numbers language-html" data-language="html"><code class="language-html">1. 内部引入-直接在当前页面中引入js代码
    示例：<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>script</span><span class="token punctuation">&gt;</span></span><span class="token script"><span class="token language-javascript">
        	console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">"js控制台"</span><span class="token punctuation">)</span>
		</span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>script</span><span class="token punctuation">&gt;</span></span>
2. 外部引入-引入外部js文件
	示例：<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>script</span> <span class="token attr-name">src</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">"</span>../js/hello.js<span class="token punctuation">"</span></span><span class="token punctuation">&gt;</span></span><span class="token script"></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>script</span><span class="token punctuation">&gt;</span></span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<p>注意：一般css放在head里，js放在body后面（html是从上往下加载的）</p>
<h2 id="3、js的3种输出方式"><a href="#3、js的3种输出方式" class="headerlink" title="3、js的3种输出方式"></a>3、js的3种输出方式</h2><pre class="line-numbers language-js" data-language="js"><code class="language-js">三种输出方式<span class="token operator">:</span>
<span class="token number">1.</span> <span class="token function">在网页上输出</span> <span class="token punctuation">(</span>相当于网页上写内容<span class="token punctuation">)</span>
        document<span class="token punctuation">.</span><span class="token function">write</span><span class="token punctuation">(</span><span class="token string">"网页上输入"</span><span class="token punctuation">)</span>    可以加载标签
<span class="token number">2.</span> <span class="token function">控制台输出</span><span class="token punctuation">(</span>一般用户debug js代码<span class="token punctuation">)</span>❤❤❤❤
        console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">"控制台打印日志"</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//类似java中的sout</span>
        快捷方式<span class="token operator">:</span> 内容<span class="token punctuation">.</span>log
<span class="token number">3.</span> 弹框❤❤
        <span class="token function">alert</span><span class="token punctuation">(</span><span class="token string">"弹框输出"</span><span class="token punctuation">)</span>
		会遮罩当前网页<span class="token punctuation">;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<h2 id="4、js的变量和数据类型"><a href="#4、js的变量和数据类型" class="headerlink" title="4、js的变量和数据类型"></a>4、js的变量和数据类型</h2><pre class="line-numbers language-js" data-language="js"><code class="language-js">【<span class="token number">1</span>】原始类型
    <span class="token number">1.</span> <span class="token function">number</span><span class="token punctuation">(</span>数值类型，无论是整数还是小数，都属于number类型<span class="token punctuation">)</span>
    <span class="token number">2.</span> <span class="token function">string</span> <span class="token punctuation">(</span>字符串<span class="token punctuation">,</span>推荐使用单引好表示<span class="token punctuation">,</span>但是双引号也可<span class="token punctuation">)</span>
    <span class="token number">3.</span> <span class="token function">boolean</span> <span class="token punctuation">(</span>布尔类型，<span class="token boolean">true</span><span class="token operator">/</span><span class="token boolean">false</span><span class="token punctuation">)</span>
    <span class="token number">4.</span> <span class="token keyword">undefined</span> <span class="token punctuation">(</span>只声明变量<span class="token punctuation">,</span>不赋值<span class="token punctuation">,</span> 即为未定义<span class="token punctuation">)</span>
	<span class="token keyword">null</span><span class="token function">（值）</span> <span class="token punctuation">(</span>空<span class="token punctuation">,</span>对象为<span class="token keyword">null</span><span class="token punctuation">,</span>undifined派生自<span class="token keyword">null</span><span class="token punctuation">,</span>console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token keyword">null</span> <span class="token operator">==</span> <span class="token keyword">undefined</span><span class="token punctuation">)</span><span class="token operator">==</span><span class="token operator">&gt;</span><span class="token boolean">true</span><span class="token punctuation">)</span>

<span class="token function">【2】引用类型</span><span class="token punctuation">(</span>对象<span class="token punctuation">)</span>
	所有对象都是继承object
    
如何获取一个变量的类型<span class="token operator">?</span>
	<span class="token keyword">let</span> type <span class="token operator">=</span> <span class="token keyword">typeof</span> 变量名称<span class="token punctuation">;</span>

js用<span class="token keyword">let</span>声明变量，用<span class="token keyword">var</span>会出现变量的溢出问题（超出作用域范围）。<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<h2 id="5、基础语法"><a href="#5、基础语法" class="headerlink" title="5、基础语法"></a>5、基础语法</h2><p>基本和JAVA相同</p>
<h3 id="1、运算符"><a href="#1、运算符" class="headerlink" title="1、运算符"></a>1、运算符</h3><pre class="line-numbers language-html" data-language="html"><code class="language-html">js运算符跟java不同之处:
1.+符号
    1.1 任何类型+string结果都是string(此时的加号就是字符串拼接)
    1.2 其余任何都能运算
            boolean: true=1, false=0
            null : 0
            undefined : NaN (not a number)
2.==(===恒等于)
==  只比较字面值,不用管类型 (常用)
=== 不仅比较字面值,还要比类型 (不常用)<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<h3 id="2、流程控制"><a href="#2、流程控制" class="headerlink" title="2、流程控制"></a>2、流程控制</h3><p>关注if判断和分支与java的不同之处：❤❤❤</p>
<pre class="line-numbers language-js" data-language="js"><code class="language-js">js中的任何类型<span class="token punctuation">,</span>在判断条件中<span class="token punctuation">,</span>自动转换成boolean
    <span class="token number">1.</span> <span class="token function">number</span><span class="token punctuation">(</span>非<span class="token number">0</span>为<span class="token boolean">true</span><span class="token punctuation">,</span> <span class="token number">0</span>为<span class="token boolean">false</span><span class="token punctuation">)</span> 
    <span class="token number">2.</span> <span class="token function">string</span><span class="token punctuation">(</span>非空串为<span class="token boolean">true</span><span class="token punctuation">,</span> 空串为<span class="token boolean">false</span><span class="token punctuation">(</span>包括‘’空字符串和undified<span class="token punctuation">)</span><span class="token punctuation">)</span>
    <span class="token number">3.</span> <span class="token keyword">null</span><span class="token punctuation">(</span>等价于<span class="token boolean">false</span><span class="token punctuation">)</span>
    <span class="token number">4.</span> <span class="token keyword">undefined</span><span class="token punctuation">(</span>等价于<span class="token boolean">false</span><span class="token punctuation">)</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<h3 id="3、循环控制"><a href="#3、循环控制" class="headerlink" title="3、循环控制"></a>3、循环控制</h3><pre class="line-numbers language-js" data-language="js"><code class="language-js"><span class="token number">2.</span> 增强<span class="token keyword">for</span>循环
		<span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">let</span> element <span class="token keyword">of</span> array<span class="token punctuation">)</span><span class="token punctuation">{</span>
			<span class="token comment">//element表示被遍历对象/集合的每个元素</span>
            需要执行的代码<span class="token punctuation">;</span>
		<span class="token punctuation">}</span>
		
<span class="token number">3.</span> 索引<span class="token keyword">for</span>循环
		<span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">let</span> index <span class="token keyword">in</span> array<span class="token punctuation">)</span><span class="token punctuation">{</span>
			<span class="token comment">//index表示 对象/数组的索引</span>
            需要执行的代码<span class="token punctuation">;</span>
		<span class="token punctuation">}</span>



<span class="token keyword">let</span> array <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token string">'a'</span><span class="token punctuation">,</span><span class="token string">'b'</span><span class="token punctuation">,</span><span class="token string">'c'</span><span class="token punctuation">]</span><span class="token punctuation">;</span> <span class="token comment">//js数组符号是中括号,不是大括号</span>

<span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">let</span> element <span class="token keyword">of</span> array<span class="token punctuation">)</span><span class="token punctuation">{</span>
    console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>element<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//打印出来的是值</span>
<span class="token punctuation">}</span>

<span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">let</span> index <span class="token keyword">in</span> array<span class="token punctuation">)</span><span class="token punctuation">{</span>
    console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>index<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//打印出来的是索引</span>
<span class="token punctuation">}</span>

<span class="token comment">// js对象</span>
<span class="token keyword">let</span> obj <span class="token operator">=</span> <span class="token punctuation">{</span>
    name <span class="token operator">:</span> <span class="token string">"张三"</span><span class="token punctuation">,</span>
    age <span class="token operator">:</span> <span class="token number">18</span><span class="token punctuation">,</span>
    married <span class="token operator">:</span> <span class="token boolean">true</span>
<span class="token punctuation">}</span>
<span class="token comment">// console.log(obj.name);</span>
<span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">let</span> index <span class="token keyword">in</span> obj<span class="token punctuation">)</span><span class="token punctuation">{</span>
    console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>index<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//打印出来的是对象的key</span>
    console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>obj<span class="token punctuation">[</span>index<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//打印的是值</span>
    console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>obj<span class="token punctuation">.</span>name<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//打印的是是值</span>
<span class="token punctuation">}</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<h2 id="6、js函数"><a href="#6、js函数" class="headerlink" title="6、js函数"></a>6、js函数</h2><h3 id="1、普通函数"><a href="#1、普通函数" class="headerlink" title="1、普通函数"></a>1、普通函数</h3><pre class="line-numbers language-js" data-language="js"><code class="language-js"><span class="token keyword">function</span>  <span class="token function">函数名</span><span class="token punctuation">(</span><span class="token parameter">参数列表</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    函数体<span class="token punctuation">;</span>
    <span class="token punctuation">[</span><span class="token keyword">return</span> 返回值<span class="token punctuation">;</span><span class="token punctuation">]</span> <span class="token comment">// 中括号意思表示内容可以省略....</span>
<span class="token punctuation">}</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span></span></code></pre>

<p>注意：</p>
<pre class="line-numbers language-js" data-language="js"><code class="language-js"><span class="token number">1.</span> 如果有返回值<span class="token punctuation">,</span>直接<span class="token keyword">return</span><span class="token punctuation">;</span>
<span class="token number">2.</span> 参数之前不用加任何关键字<span class="token punctuation">;</span>
<span class="token number">3.</span> 调用函数时<span class="token punctuation">,</span> 实参个数不必跟形参个数一致<span class="token punctuation">;</span>
<span class="token number">4.</span> 函数内部有一个隐式变量 <span class="token function">arguments</span><span class="token punctuation">(</span>arguments是数组<span class="token punctuation">,</span> 会接收所有传入的参数<span class="token punctuation">)</span>
<span class="token number">5.</span> js函数没有重载机制<span class="token punctuation">;</span> <span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<p>例子：</p>
<pre class="line-numbers language-js" data-language="js"><code class="language-js"><span class="token keyword">function</span> <span class="token function">methord2</span><span class="token punctuation">(</span><span class="token parameter">name<span class="token punctuation">,</span>age</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">"name-age:"</span><span class="token punctuation">,</span>name<span class="token punctuation">,</span>age<span class="token punctuation">)</span>
    <span class="token comment">//内置的对象：arguments,可以获取出入函数的所有值</span>
    <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">let</span> data <span class="token keyword">of</span> arguments<span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token comment">//获取动态出入的所有参数</span>
        console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>data<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token comment">//name-age: zhagnsan 18</span>
<span class="token comment">//methord2("zhagnsan",18);</span>
<span class="token function">methord2</span><span class="token punctuation">(</span><span class="token string">"lisi"</span><span class="token punctuation">,</span><span class="token number">20</span><span class="token punctuation">,</span><span class="token string">"北京"</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>



<h3 id="2、匿名函数"><a href="#2、匿名函数" class="headerlink" title="2、匿名函数"></a>2、匿名函数</h3><p>匿名函数通常与事件结合使用</p>
<pre class="line-numbers language-js" data-language="js"><code class="language-js"><span class="token number">1.</span> 命名函数
    <span class="token keyword">function</span> <span class="token function">函数名</span><span class="token punctuation">(</span><span class="token parameter">参数列表</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        函数体
    <span class="token punctuation">}</span>
<span class="token number">2.</span> 匿名函数
    <span class="token function-variable function">变量</span> <span class="token operator">=</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token parameter">参数列表</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        函数体
    <span class="token punctuation">}</span>

匿名函数注意点<span class="token operator">:</span>
    <span class="token number">1.</span> 在js中<span class="token punctuation">,</span>函数也是一种特殊的变量类型
    <span class="token number">2.</span> 匿名函数必须给变量

  匿名函数的运用场景<span class="token operator">:</span>
    <span class="token number">1.</span> 对象定义
    <span class="token number">2.</span> 事件注册<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<pre class="line-numbers language-js" data-language="js"><code class="language-js">
<span class="token keyword">let</span> obj <span class="token operator">=</span> <span class="token punctuation">{</span>
    name <span class="token operator">:</span> <span class="token string">"张三"</span><span class="token punctuation">,</span>
    age <span class="token operator">:</span> <span class="token number">18</span><span class="token punctuation">,</span>
    <span class="token function-variable function">speak</span> <span class="token operator">:</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token parameter">x</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">// 匿名函数写法</span>
        console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span>name <span class="token operator">+</span> <span class="token string">"说"</span> <span class="token operator">+</span> x<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span><span class="token punctuation">,</span>
    <span class="token function">eat</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span> <span class="token comment">// 命名写法</span>
        console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span>name <span class="token operator">+</span> <span class="token string">"正在吃饭"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
obj<span class="token punctuation">.</span><span class="token function">speak</span><span class="token punctuation">(</span><span class="token string">'今天天气真好'</span><span class="token punctuation">)</span>
obj<span class="token punctuation">.</span><span class="token function">eat</span><span class="token punctuation">(</span><span class="token punctuation">)</span>



<span class="token keyword">let</span> <span class="token function-variable function">method02</span> <span class="token operator">=</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">"匿名函数"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token function">method02</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// 通过变量名调用</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<h2 id="7、js事件"><a href="#7、js事件" class="headerlink" title="7、js事件"></a>7、js事件</h2><pre class="line-numbers language-js" data-language="js"><code class="language-js"><span class="token number">1.</span> 点击事件：
        <span class="token number">1.</span> onclick：单击事件
        <span class="token number">2.</span> <span class="token function">ondblclick：双击事件</span> <span class="token punctuation">(</span>double<span class="token operator">:</span> 时间间隔很短两次单击<span class="token punctuation">)</span>
        
<span class="token number">2.</span> 焦点事件
        <span class="token number">1.</span> <span class="token function">onblur：失去焦点</span><span class="token punctuation">(</span>绑定鼠标离焦事件<span class="token punctuation">)</span>
        <span class="token number">2.</span> onfocus<span class="token operator">:</span><span class="token function">元素获得焦点。</span><span class="token punctuation">(</span>绑定鼠标聚焦事件<span class="token punctuation">)</span>

<span class="token number">3.</span> 加载事件：
        <span class="token number">1.</span> onload：页面加载完成后立即发生。

<span class="token number">4.</span> 鼠标事件：
        <span class="token number">1.</span> onmousedown	鼠标按钮被按下。
        <span class="token number">2.</span> onmouseup	鼠标按键被松开。
        <span class="token number">3.</span> onmousemove	鼠标被移动。
        <span class="token number">4.</span> onmouseover	鼠标移到某元素之上。
        <span class="token number">5.</span> onmouseout	鼠标从某元素移开。
        
<span class="token number">5.</span> 键盘事件：
		<span class="token number">1.</span> onkeydown	某个键盘按键被按下。	
		<span class="token number">2.</span> onkeyup		某个键盘按键被松开。
		<span class="token number">3.</span> onkeypress	某个键盘按键被按下并松开。

<span class="token number">6.</span> 改变事件
        <span class="token number">1.</span> onchange	域的内容被改变。

<span class="token number">7.</span> 表单事件：
        <span class="token number">1.</span> onsubmit	提交按钮被点击。<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<pre class="line-numbers language-js" data-language="js"><code class="language-js"><span class="token comment">// 使用</span>
<span class="token number">1.</span> 命名函数绑定
    <span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">.</span> 定义一个命名函数<span class="token punctuation">;</span>
    <span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">.</span> 给标签添加属性<span class="token operator">:</span>on事件名 <span class="token operator">=</span> <span class="token string">"函数调用"</span><span class="token punctuation">;</span>
	效果<span class="token operator">:</span> 事件被触发的时候<span class="token punctuation">,</span>函数就会被调用
<span class="token number">2.</span> 匿名函数绑定❤❤❤
    <span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">.</span> 用js代码找到标签对象<span class="token punctuation">;</span>
    <span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">.</span> 标签对象<span class="token punctuation">.</span>on事件名 <span class="token operator">=</span> 匿名函数<span class="token punctuation">;</span>
    效果<span class="token operator">:</span> 事件被触发的时候<span class="token punctuation">,</span>函数就会被调用
    匿名函数更加常用<span class="token punctuation">,</span>更加解耦 



    <span class="token operator">&lt;</span>input type<span class="token operator">=</span><span class="token string">"button"</span> value<span class="token operator">=</span><span class="token string">"普通函数"</span> onclick<span class="token operator">=</span><span class="token string">"method01('hehe')"</span><span class="token operator">&gt;</span> <span class="token operator">&lt;</span>br<span class="token operator">&gt;</span>
    <span class="token operator">&lt;</span>input type<span class="token operator">=</span><span class="token string">"button"</span> value<span class="token operator">=</span><span class="token string">"匿名函数"</span> id<span class="token operator">=</span><span class="token string">"btn"</span><span class="token operator">&gt;</span> <span class="token operator">&lt;</span>br<span class="token operator">&gt;</span>
        
        <span class="token keyword">function</span> <span class="token function">method01</span><span class="token punctuation">(</span><span class="token parameter">a</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>a<span class="token punctuation">)</span>
    <span class="token punctuation">}</span>

    <span class="token comment">//DOM: 这个方法可以看成id选择器</span>
        <span class="token comment">// btn表示 id选择器 定位到的 标签对象</span>
    <span class="token keyword">let</span> btn <span class="token operator">=</span> document<span class="token punctuation">.</span><span class="token function">getElementById</span><span class="token punctuation">(</span><span class="token string">"btn"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    btn<span class="token punctuation">.</span><span class="token function-variable function">onclick</span> <span class="token operator">=</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">"xixi"</span><span class="token punctuation">)</span>
    <span class="token punctuation">}</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<pre class="line-numbers language-js" data-language="js"><code class="language-js"><span class="token comment">// 出现的问题</span>

问题<span class="token operator">:</span> btn是空的<span class="token punctuation">,</span>就意味着找不到id<span class="token operator">=</span>btn的标签
            做的事件<span class="token operator">:</span>
                script标签移动body标签之前

             原因<span class="token operator">:</span>
                浏览器加载网页从上至下<span class="token punctuation">,</span> 执行<span class="token keyword">get</span>函数的时候<span class="token punctuation">,</span>body标签还没加载

             解决方案<span class="token operator">:</span>
                等页面加载完毕了<span class="token punctuation">,</span>再执行<span class="token keyword">get</span>函数就行了

                <span class="token operator">-</span><span class="token operator">&gt;</span> 第二个事件<span class="token operator">:</span> 唯一不需要用户触发的事件<span class="token punctuation">,</span>是浏览器加载网页结束时触发
                    window<span class="token punctuation">.</span>onload<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<h2 id="8、内置对象"><a href="#8、内置对象" class="headerlink" title="8、内置对象"></a>8、内置对象</h2><h3 id="1、String"><a href="#1、String" class="headerlink" title="1、String"></a>1、String</h3><pre class="line-numbers language-text" data-language="text"><code class="language-text">1. 构造字符串可以使用
    a. 双引号
    b. 单引号
    c. 反引号(重音符) 键盘左上角 esc下面 (es6模板字符串)
       优势:在字符串拼接时，可直接使用${变量}引入外部变量值
    
2. 字符串常用方法
    substring(startIndex,endIndex) 提取字符串中两个指定的索引号之间的字符(包头不包尾)
    toLowerCase() 把字符串转换为小写。
    toUpperCase() 把字符串转换为大写。
    split("指定字符切割") 把字符串分割为字符串数组。
    trim() 去掉首尾空格<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>



<h3 id="2、Array数组对象"><a href="#2、Array数组对象" class="headerlink" title="2、Array数组对象"></a>2、Array数组对象</h3><pre class="line-numbers language-js" data-language="js"><code class="language-js"><span class="token number">1.</span> <span class="token keyword">let</span> array <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Array</span><span class="token punctuation">(</span><span class="token string">'a'</span><span class="token punctuation">,</span><span class="token string">'b'</span><span class="token punctuation">,</span><span class="token string">'c'</span><span class="token punctuation">)</span>
<span class="token number">2.</span> <span class="token keyword">let</span> array <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token string">'a'</span><span class="token punctuation">,</span><span class="token string">'b'</span><span class="token punctuation">,</span><span class="token string">'c'</span><span class="token punctuation">]</span>  <span class="token comment">// 推荐, 中括号</span>
注意事项：
    a<span class="token punctuation">.</span>数组中的元素可以不是同一种类型
    b<span class="token punctuation">.</span>数组可以动态扩容<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span></span></code></pre>



<h3 id="3、Date日期对象"><a href="#3、Date日期对象" class="headerlink" title="3、Date日期对象"></a>3、Date日期对象</h3><pre class="line-numbers language-js" data-language="js"><code class="language-js"><span class="token number">1.</span> 创建对象
   <span class="token keyword">let</span> date <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> 获取当前时间时间 <span class="token comment">//Sun May 24 2020 14:38:34 GMT+0800 (中国标准时间:东八区)</span>
<span class="token number">2.</span> 常用方法
    <span class="token function">toLocaleString</span><span class="token punctuation">(</span><span class="token punctuation">)</span> 转换为本地日期格式的字符串  <span class="token comment">//2021/8/28下午9:00:06</span>
    <span class="token function">getFullYear</span><span class="token punctuation">(</span><span class="token punctuation">)</span> 获取日期中的year <span class="token comment">// 2021</span>
    <span class="token function">getMonth</span><span class="token punctuation">(</span><span class="token punctuation">)</span>   获取日期中的month <span class="token comment">// 值：0-11</span>
    <span class="token function">getDate</span><span class="token punctuation">(</span><span class="token punctuation">)</span>    获取日期中的号 <span class="token comment">// 24</span>
    <span class="token function">getTime</span><span class="token punctuation">(</span><span class="token punctuation">)</span>   <span class="token function">获取时间毫秒值</span><span class="token punctuation">(</span>时间原点<span class="token operator">:</span> <span class="token number">1970</span>年<span class="token number">1</span>月<span class="token number">1</span>号<span class="token number">0</span>时分秒<span class="token punctuation">)</span> <span class="token punctuation">;</span><span class="token comment">//// 1970年~今毫秒值</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>



<h3 id="4、Math数学对象"><a href="#4、Math数学对象" class="headerlink" title="4、Math数学对象"></a>4、Math数学对象</h3><pre class="line-numbers language-js" data-language="js"><code class="language-js"><span class="token number">1.</span> 四舍五入 <span class="token function">round</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token number">2.</span> 向下取整 <span class="token function">floor</span><span class="token punctuation">(</span><span class="token punctuation">)</span>  地板
<span class="token number">3.</span> 向上取整 <span class="token function">ceil</span><span class="token punctuation">(</span><span class="token punctuation">)</span>  天花板
<span class="token number">4.</span> 产生随机数 <span class="token function">random</span><span class="token punctuation">(</span><span class="token punctuation">)</span> ：返回 <span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">,</span><span class="token number">1</span><span class="token punctuation">)</span> <span class="token function">之间的随机数</span><span class="token punctuation">(</span>包含<span class="token number">0</span>不包含<span class="token number">1</span><span class="token punctuation">)</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span></span></code></pre>



<h3 id="5、js全局函数"><a href="#5、js全局函数" class="headerlink" title="5、js全局函数"></a>5、js全局函数</h3><pre class="line-numbers language-js" data-language="js"><code class="language-js">js全局函数不需要通过任何对象间接调用，可直接调用<span class="token punctuation">;</span>
常见的全局函数如下：
<span class="token function">parseInt</span><span class="token punctuation">(</span>str<span class="token punctuation">)</span>：输入数据转int类型
<span class="token function">parseFloat</span><span class="token punctuation">(</span>str<span class="token punctuation">)</span>：输入数据转小数类型
<span class="token function">encodeURI</span><span class="token punctuation">(</span>word<span class="token punctuation">)</span>：编码字符串
<span class="token function">decodeURI</span><span class="token punctuation">(</span>result2<span class="token punctuation">)</span>：解码字符串<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>


                
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